1. Field of the Invention
The present invention relates to a probe card, and more particularly, to a probe card having less contact stress applied to the wafer.
2. Description of the Prior Art
For testing high density and high-speed electrical elements such as large-scale integrated (LSI) and very large-scale integrated (VLSI) circuits, a probe card is commonly employed. The probe card includes tiny, precise contact structures to contact with dies on a wafer, thus to establish an electric connection for carrying out the test.
FIG. 1 shows a conventional test system of probe card. A semiconductor test system 10 sends out test signals through a cable 11 to a tester 12. The test signals are transmitted to a load board 13 later. The load board 13 transmits the test signals to a probe card 14. The probe card 14 transmits the test signals to a plurality of tiny, precise contact sites 15. A handler 17 bears a wafer 16 for establishing an electric connection between the contact sites 15 and dies (not shown) on the wafer 16 by moving the handler 17, such that the dies on the wafer 16 receive the test signals for carrying out the test. When the test is finished, the contact sites 15 receive the test result and send it back to the semiconductor test system 10 through a reverse path as mentioned above.
Referring to FIG. 2, Taiwan Patent issued no. 00587699, entitled “Probe Card having a Fixed Ring,” discloses a conventional probe card. A probe card 20 comprises a fixed ring 21, a circuit board (not shown) arranged on the top surface of the fixed ring 21, an isolated ring 22 arranged on the bottom surface of the fixed ring 21, where a plurality of contact pins 23 having the same pitch with one another pass through the isolated ring 22. Each contact pin 23 includes a tip portion 24 directing downward, and the tip portion 24 corresponds to the contact sites 15 as mentioned above. The tip portion 24 will electrically connect to a pad (not shown) of the dies of the wafer for carrying out the test.
When the tip portion 24 contacts the pad, generally probe marks will be generated due to a contact stress; however, if the contact stress applied to the pad is too large, the probe marks will exceed the range within the pad and thus harm the die. In addition, the exceeding contact stress may damage the circuit or semiconductor region of the die under the pad, causing the die to be defective, and consequently the test result fails.
Therefore, it would be advantageous to provide a novel probe card that overcomes the defects of the prior art.